The present invention relates generally to the field of information display and, in particular, to a system and method for the display of hierarchical information structures.
There are many circumstances where trees must be represented as nested lists rather than in graphic form. One method of displaying a nested list is by indenting child nodes under the parent nodes. An example of an application that requires the display of a nested list is a display of thread structures within electronic mail discussion lists. In archives of intensive or broad-membership e-mail lists, many threads contain many messages. Fully nested outline representations of such threads, with each message indented under its predecessor, can be extremely wide. Also, it is desirable to be able to embed textual material, including author, date, time and even message-initial fragments in such displays. When this is done, the fully nested displays may be untenable.
Some conventional e-mail display methods fold back the child nodes to a left margin after a predetermined number of indentations is reached. However, such a display scheme masks the structure of the thread.
Other conventional e-mail archive applications limit the width of the display. For example, Hypermail(copyright) provides a xe2x80x9csubjectxe2x80x9d listing in which messages with the same subject line are listed in chronological order. Egroups(copyright) provides a subject-based listing in which two levels are used, with messages indented under the corresponding parent if that results in only two levels and if the child node is received very close in time to the parent node.
U.S. Pat. No. 5,065,347 describes a method and apparatus for displaying hierarchic folders to a user-specified width and for xe2x80x9cfolding backxe2x80x9d the display, using icons when the user specified width is reached. All documents cited herein, including the foregoing, are incorporated herein by reference in their entireties.
A first embodiment of the method and apparatus of the present invention provides a tree structure which does not indent single children within the tree. More particularly, this first embodiment forms a semi-linear tree representation by applying a recursive procedure to the nodes of the tree starting at the root. If a node has multiple successors, then and only then are successors indented, with each successor separated by a divider.
A second embodiment of the method and apparatus of the present invention is an extension of the first embodiment and uses an application-based criteria that determines which subtrees of nodes with multiple children are listed first. This second embodiment lists smaller subtrees first.